In conventional copying apparatus or the like, an elongated light source in the form of a rod is used for illuminating originals. The elongated light source, such as a fluorescent lamp, has an uneven distribution of illumination intensities in the longitudinal direction thereof. The illumination intensity of the area illuminated with the light source is substantially uniform at the center portion in the longitudinal direction of the source but is lower in the vicinity of opposite end portions. Therefore, a light source sufficiently greater in length than the area to be illuminated may be employed so as to give the area a uniform distribution of illumination intensities, but the light source will then render the apparatus larger.
To overcome this problem, Unexamined Japanese Utility Model Publication No. SHO 54-174343 discloses an illumination device which comprises a fluorescent lamp serving as a light source for illuminating originals and a trapezoidal light blocking plate interposed between the lamp and the surface of the original and having an upper side which has the same length as the uniform light emitting portion of the lamp. Unexamined Japanese Utility Model Publication SHO No. 59-9673 proposes to dispose a reflecting plate at one side of a tubular light source for illuminating an original at the other side thereof, the reflecting plate having a small reflectance at its middle portion with respect to the longitudinal direction of the light source and a great reflectance at its opposite ends.
However, the devices of the two publications are adapted to give a uniform illumination intensity distribution by decreasing the illumination intensity at the middle portion and therefore have the problem of being low in illumination efficiency and deficient in the quantity of light available at the position to be illuminated.